Section 24-3

1. Nuclear Fission • Stability of elements is best around a mass number of 60. • Atoms with a mass number greater than 60 tend to gain stability by fragmenting. • The splitting of nuclei into fragments is known as nuclear fission. • Fission is accompanied with a very large release of energy. Section 24-3

2. Nuclear Fission • Nuclear power plants use fission to produce electricity by striking uranium-235 with neutrons. Section 24-3

3. Nuclear Fission (cont.) • Each fission of U-235 releases three additional neutrons. • Each of those neutrons can release three more neutrons. • The self-sustaining process is called a chain reaction. • http://glencoe.mcgraw-hill.com/sites/007874637x/student_view0/chapter24/concepts_in_motion.html Section 24-3

4. Nuclear Fission (cont.) Section 24-3

5. Nuclear Fission (cont.) • There must be sufficient mass to get the chain reaction started. If not the neutrons escape before striking other nuclei. • Without sufficient mass, neutrons escape from the sample before starting a chain reaction. • Samples with enough mass to sustain a chain reaction are said to have critical mass. • Samples with mass that is much greater than the critical mass have a reaction that escalates at a violent level and can cause a nuclear explosion. This is the supercritical mass. Section 24-3

6. Nuclear Fission (cont.) http://www.youtube.com/watch?v=qybUFnY7Y8w Section 24-3

7. Nuclear Reactors • Nuclear fission produces the energy generated by nuclear reactors. • The fission within a reactor is started by a neutron-emitting source and is stopped by positioning the control rods to absorb virtually all of the neutrons produced in the reaction. Section 24-3

8. Nuclear Reactors (cont.) • The reactor core contains a reflector that reflects neutrons back into the core, where they react with fuel rods. • Nuclear reactors produce highly radioactive nuclear waste. • Breeder reactorsproduce more fuel than they consume. Section 24-3

9. Nuclear Reactors (cont.) Section 24-3

10. Nuclear Fusion • It is possible to bind together two or more lighter elements (mass number less than 60). • The combining of atomic nuclei is called nuclear fusion. • Nuclear fusion is capable of releasing very large amounts of energy. • The sun is powered by the fusion of hydrogen atoms to form helium atoms and a lot of energy. Section 24-3

11. Nuclear Fusion (cont.) • Fusion has several advantages over fission. • Lightweight isotopes are abundant. • Fusion products are not radioactive. • However, fusion requires extremely high energies to initiate and sustain a reaction. Section 24-3

12. Nuclear Fusion (cont.) • Fusion reactions are also known as thermonuclear reactions. • Many problems must be solved before nuclear fusion is a practical energy source. Section 24-3

13. A B C D Section 24.3 Assessment Bombarding a nuclei with charged particle in order to create new elements is called ____. A.nuclear conversion B.nuclear decay C.induced decay D.induced transmutation Section 24-3

14. A B C D Section 24.3 Assessment Thermonuclear reactions involve: A.splitting nuclei into smaller fragments B.fusing nuclei together to form larger particles C.bombarding nuclei with charged particles D.generating electricity in a nuclear reactor Section 24-3